Interobserver agreement of Medical Research Council sum-score and handgrip strength in the intensive care unit

INTRODUCTION

Muscle weakness often complicates critical illness and is associated with devastating short- and long-term consequences. For interventional studies, reliable measurements of muscle force in the intensive care unit (ICU) are needed.

METHODS

To examine interobserver agreement, two observers independently measured Medical Research Council (MRC) sum-score (n = 75) and handgrip strength (n = 46) in a cross-sectional ICU sample.

RESULTS

The intraclass correlation coefficient (ICC) for MRC sum-score was 0.95 (0.92-0.97). The kappa coefficient for identifying "significant weakness" (MRC sum-score <48, MRC subtotal upper limbs <24) and "severe weakness" (MRC sum-score <36) was 0.68 ± 0.09, 0.88 ± 0.07, and 0.93 ± 0.07, respectively. The ICC for left and right handgrip strength was 0.97 (0.94-0.98) and 0.93 (0.86-0.97), respectively.

CONCLUSIONS

Interobserver agreement on MRC sum-score and handgrip strength in the ICU was very good. Agreement on "severe weakness" (MRC sum-score <36) was excellent and supports its use in interventional studies. Agreement on "significant weakness" (MRC sum-score <48) was good, but even better using the equivalent cut-off in the upper limbs. It remains to be determined whether this may serve as a substitute.